1. Field of the Invention
The present invention relates to a key switch, a keyboard comprising a plurality of key switches, and a portable information processing unit with a keyboard, and more particularly to a structure of a portable information processing unit allowing the height of key switches on the keyboard to be lowered in a closed state of a cover thereof.
2. Description of the Related Art
One principal problem of a portable information processing unit, such as a notebook-size personal computer which has come into widespread use, is how to accomplish size reduction thereof, particularly a reduction of a height (thickness) thereof, for the purpose of making it more convenient to carry. Referring to Figures, as one example, a description will be made hereinbelow of a structure of a notebook-size personal computer. FIG. 9 is a perspective view schematically showing the whole structure of a notebook-size personal computer. In this figure, a housing of a personal computer 1 is composed of a main body 11a for accommodating a keyboard 12 and a cover 11b which mounts therein a display 19, such as a liquid crystal panel. The cover 11b is openable and closable about a hinge 11c fitted in one side of the main body 11a, to a desired angle a between 90 degrees and 180 degrees. When selectively holding down a plurality of key switches 129 arranged on the keyboard 12 according to a given rule, the letters and symbols corresponding to the pressed key switches 129 appear on the display 19 or the results of the designated processing appear thereon.
FIG. 10 is a partial perspective view showing a keyboard to be used in such a notebook-size personal computer 1, including an exploded illustration of one key switch and a cross section of a principal component. As illustrated, the keyboard 12 is composed of a membrane switch composite 121, in which switching areas 121a are assigned to given locations, a plurality of key switches 129 disposed in positions corresponding to the switching regions 121a, and a unitary molded base 123 common to the plurality of key switches 129. The membrane switch composite 121 includes two insulating films stacked and spaced from each other by a small gap. Each of the key switches 129 includes one rubber actuator 122, two links 124 and a key top 125. A plurality of electric contacts (the areas 121a are indicative of their positions) are made on the respective inner surfaces of the insulating films in the membrane switch composite 121. The rubber actuator 122 is disposed on the membrane switch composite 121 so as to be in corresponding relation to the switching areas 121a. The membrane switch composite 121 is fixed onto a bottom plate 11a' of the main body 11a.
The rubber actuator 122 with a bowl-like configuration is equipped with a flange 122a formed at the circumferential portion of its open end, and is inserted into a through hole 123b of the molded base 123 from the direction indicated by an arrow A. The rubber actuator 122 develops a reversible deformation when its head portion is pressed with a given pressure, so that its open end surface depresses the membrane switch 121, which accomplishes the connection of the electric contacts formed in the membrane switch 121. On release from this depression, the rubber actuator 122 is restorable from its deformed state, thereby to break the electric contact connection.
The molded base 123 has a planar dimension substantially equal to that of the membrane switch 121, where a plurality of through holes 123b are made with each corresponding to each of the switching areas 121a of the membrane switch 121. On the base 123 there is installed a wall 123a surrounding an area around each of the through holes 123b. The rubber actuator 122, inserted into the through hole 123b from the arrow A direction, is located so that its head portion 122b protrudes upwardly from a bottom surface 123d of the base 123. The rubber actuator 122 is fixedly secured onto the base mold 123 in the manner that its flange portion 122a is fitted in a step around the through hole 123b. On the upper surface of the bottom wall 123d of the base 123, in the vicinities of four corners of each of areas enclosed by the wall 123a, there are disposed two pairs of hooks 123c each comprising a column section 123c.sub.-1 and an arm section 123c.sub.-2 linked to make an L-shaped configuration. The two pairs of hooks 123c are fixed onto the base mold 123 in a state where they sit, back to back with each other and with the tip portions of the arm sections 123c.sub.-2 the respective opposed portions of the wall 123a.
Each of the pair of links 124 is composed of a connection section 124a and a pair of arms 124c extending at right angles from both ends of the connection section 124a. The length of the connection section 124a is slightly shorter than the separation a2 between each pair of hooks 123c fixed on the base 123. Each of the arms 124c has a projection 124b and a projection 124d on its outside surface. The projection 124b has a diameter to allow the insertion thereof into a gap between the arm section 123c.sub.2 of the hook 123c and the bottom surface 123d of the base mold 123, whereas the projection 124d has a diameter to allow the fitting in a bearing hole made in a hook 125c fixed onto the inner top surface of the key top 125.
Accordingly, the projection 124b on each of arms 124c of the link 124 is put into the space between the arm section 123c.sub.-2 of the corresponding hook 123c and the base 123 as indicated by an arrow B, the link 124 then being rotatable about the axis of the projection 124b. On the other hand, as indicated by an arrow D, the projection 124d on each of the arms 124c is fitted in the bearing hole of the corresponding hook 125c (indicated with a dotted line) formed inside the key top 125. Whereupon, the link 124 is rotatable about the axis of the projection 124d.
With this structure, the plural key tops 125 are coupled through the respective links 124 to the base 123. Each of the key tops 125 has a plane size substantially equal to that of each area surrounded by the wall 123a of the base 123, and in general its outer surface 125a has a configuration to make a portion of a square conical surface. A projection 125b which is rod-like or cylindrical, for example, is formed in the vicinity of the center inside of the key top 125.
A keyboard comprising the above-mentioned components is assembled as follows. First, the membrane switch 121 is mounted on the bottom surface 11a' of the main body 11a. Secondly, for example, the rubber actuator 122 is mounted on each of the switching areas 121a of the composite membrane switch 121, and subsequently the base 123 is fixed onto the main body 11a. The rubber actuator 122 mounted at a given portion of the composite membrane switch 121 is positioned by the base 123. Then, the base 123 and each of the key tops 125 are connected through the two links 124. Thus, the keyboard 12 as shown in FIG. 9 is completed with the plurality of key switches 129 provided.
FIGS. 11A and 11B show cross sections of the keyboard 12. FIG. 11A shows a non-operated state of the keyboard 12 (no depression of the key top), while FIG. 11B illustrates an operated state thereof (depression of the key top). In FIG. 11A, the tip surface of the projection 125b of the key top 125 is brought into contact with the head portion 122b of the rubber actuator 122. In this state, the switching area 121a of the membrane switch composite 121 is in a non-contact state as illustrated. When the key top 125 is depressed as shown in FIG. 11B, the projections 124b in the connection section sides of the two link 124 slide in directions of separating from each other (the direction of approaching the corresponding wall 123a) between the bottom surface 123d of the base 123 and the arm 123c.sub.-2 of the hook 123c. Thus, the depression of the projection 125b of the key top 125 against the head portion 122b of the rubber actuator 122 continues to create the deformation of the rubber actuator 122. At the time that the depression of the key top 125 reaches a given position, the rubber actuator 112 develops the maximum deformation so that the switching area 121a comes into the connecting condition. Commonly, the hollow rubber actuator 122 is rapidly bent in a ringlike form at the portion in the vicinity of the flange 122a (called reversible inversion), and the key top 125 reaches the maximum depression position. A click sensation is given in the process of this depression.
On releasing the key top 125 from the depressing operation, the rubber actuator 122 restores, or recovers, to its original shape as shown in FIG. 11A due to its own elastic force. In consequence, the projections 124b in the connection section sides of the links 124 slide in directions of approaching each other (the directions of separating from the corresponding walls 123a) between the bottom surface 123d of the base 123 and the arm 123c.sub.-2 of the hook 123c, so that the key top returns to its initial position. Thus, with the depression of the key top 125 or with the releasing from the depression, an electrical on and off operation takes place in the switching area 121a.
FIGS. 12A and 12B are cross-sectional views showing another keyboard to be used for the notebook-size personal computer as shown in FIG. 9, where the keyboard is cut in one key switch area and extracted. FIG. 12A shows a non-operated state of the key board, while FIG. 12B illustrates an operated condition thereof. In FIG. 12A, a keyboard 13 is made up of a composite membrane switch 121 fixed onto a bottom plate 11a' of a main body 11a and a plurality of key switches 139 fixedly disposed at given portions of the membrane switch composite 121, even a single key switch is shown. Each of the key switches 139 comprises a tongue-like actuator 132 corresponding to one of a plurality of contacts formed on the composite membrane switch 121, a base 133 to which one end portion of the actuator 132 is fixed, and a key top 134 mounted on the base 133 so as to be movable by a given stroke in a depressing direction. Each of the composite membrane switch 121 and the base 133 is one member common to the plurality of key switches 139, and the plurality of key switches 139 are disposed at the corresponding positions defined therein.
Each of the actuators 132 is constructed with a spring metallic plate and is provided with a contact pressing section 132b for pressing the corresponding contact of the composite membrane switch 121. In addition, the actuator 132 having one end portion fixed to the base 133 extends from the contact pressing section 132b toward the other free end portion 132c to gradually separate from the composite membrane switch 121. The base 133 has areas each corresponding to each of the key switches 139 and provided with a square through hole 133a in each of the areas. A plurality of projections 133b are formed on the upper portion (the portion most remote from the composite membrane switch) of the circumferential side wall surface of the through hole 133a. The key top 134 has a configuration similar to that shown in FIG. 9 and its outer surface 134a makes a square conical surface. Further, a projection 134b which is circular, for example, is provided in an inner central portion of the key top 134. In general, at the circumference of the projection 134b there is placed a sleeve section 134c which can be engaged into the through hole 133a of base 133 to be slidable. A plurality of projections 134d are formed on the outer surface of the sleeve section 134c. In a state where the sleeve section 134c is inserted into the through hole of the base 133, the key top 134 is movable by a given stroke in the insertion direction. The upper limit of the movement thereof is the position where the projection 133b in the base 133 side comes into contact with the projection 134d in the key top 134 side.
The assembly of the key top 134 is as follows. That is, first, the actuator 132 is amounted on a given location of the base 133. Secondly, the composite membrane switch 121 is mounted on the bottom plate 11a' of the housing main body 11a. Subsequently, for example, the base 133 is fixed onto the housing main body 11a so that the contact pressing section 132b of the tongue-like actuator 132 is located at each of the switching areas 121a of the composite membrane switch 121. Finally, the plurality of key tops 134 are set at given positions of the base 133, thus completing the keyboard 13, as now equipped with the key switches 139 whose number equals the number of contacts of the membrane switch composite 121.
FIG. 12A shows a case in which the key top 134 is at the upper limit position. The free end portion 132c of the actuator 132 is in the state with being placed into contact with the lower end surface of the projection 134b of the key top 134. FIG. 12B illustrates a state where the key top 134 is depressed up to the lower limit. The projection 134b presses the free end portion 132c of the actuator 132 so that the actuator 132 deforms. At the same time, the contact pressing section 132b presses the switching portion 121a of the composite membrane switch 121, with the result that an electrical connection is produced in the switching area 121a. On releasing from the depression (i.e., depressed state), the key top 134 returns to the initial state as shown in FIG. 12A due to the elastic force of the actuator 132. With the above operation, the key top 134 presses the free end portion 132c, separated by a plane projection distance e from the contact pressing section 132b, of the actuator 132. Accordingly, owing to the so-called lever principle, a completed connection in the switching area 121a is possible with a weak pressing force.
In the prior art key switches 129 and 139 on the above-described keyboards 12 and 13, the key top upper surface protrudes upwardly from the base , including the drop quantity (i.e., stroke length) at the depression. However, the respective thicknesses of the housing main body 11a and the cover 11b are required to be set so that the surface of the display 19 does not come into contact with the top surfaces of the key tops even when the cover 11b takes (i.e. is in) the closed condition. Accordingly, the thickness of the notebook-size personal computer 1 main body increases, with the result that difficulty is encountered to meet the customer's requirements for the size reduction.